Scientists have discovered a set of nerve cells in the brain crucial for our ability to sleep and controlling our body temperature.
How sleep works in the human brain has largely remained a mystery, with some people seemingly being able to fall asleep in an instant, while others take significantly longer.
Now, however, research published to Nature Communications by a team of scientists appears to confirm the discovery of the brain’s ‘sleep switch’, two decades after it was first suggested.
The team from the Department of Neurology at Beth Israel Deaconess Medical Center in the US revealed that the cells – located in a region of the hypothalamus called the ventrolateral preoptic nucleus (VLPO) – are essential for us to drift off.
Working with genetically engineered mice, the team artificially activated the VLPO neurons using several different tools. In one experiment, the team activated the neuron cells using a laser beam technique called optogenetics that makes them fire. In another test, the researchers used a chemical that selectively activates the VLPO neurons.
In both tests, they found they were crucial in the animals falling asleep. This confirmed previous findings from the team led by Clifford Saper that damage to these neurons can cause insomnia.
Most interestingly, these results completely contradict another study published in 2017, which found that stimulating VLPO neurons resulted in the mice becoming alert.
Explaining this contradiction, Saper said: “We found that when the VLPO cells are stimulated one to four times per second, they fire each time they are stimulated, resulting in sleep.
“But, if you stimulate them faster than that, they begin to fail to fire and eventually stop firing altogether. We learned our colleagues in the other lab were stimulating the cells 10 times per second, which was actually shutting them off.”
Another interesting finding in the research was how VLPO neurons control body temperature – or, more specifically, how they make us colder when activated.
In the mice, VLPO activation saw a drop in body temperatures by as much as six degrees Celsius. “We thought that this is why people need to curl up under a warm blanket to get to sleep,” Saper said.
The team proposed that excessive firing of these same neurons may be responsible for the prolonged sleep and decline in body temperature in animals that hibernate.